ES2992805T3 - Bone joint implants - Google Patents

Abstract

A bone articulation implant (1) has a proximal portion (120) for translational movement about the trapezium at a first carpometacarpal joint and a distal portion (110) for intramedullary engagement at the first metacarpal bone. An articulating engagement (103, 121, 123) is for multiaxial movement with translational movement about a bone in one portion (120) and rotation in the other portion (110) about the articulating engagement (121, 103). A flange (105) extends radially and about the engagement to limit relative rotational movement of the proximal and distal portions about the engagement, and to provide resilience for contact between the proximal and distal portions. The flange has a contoured surface (101) that mates with a bearing surface (125) of the proximal portion (122) upon articulation of the portions in use to extreme positions. The flange (105) is included in an insert (100) in a stem (111) of the distal part (110), the flange extending proximally to the stem (111) and prohibiting contact between the proximal part (120) and the stem (111) during articulation. (Automatic translation with Google Translate, no legal value)

Description

DESCRIPTION

Bone joint implants

Introduction

The invention relates to an implant for a bone joint. In some examples it relates to implants in which there are multiple axes of rotation, such as those in which there is a double-axis hemiarthroplasty with two axes of rotation as for example in the hand or elbow. However, in other aspects the invention relates to a uniaxial implant such as a hip joint implant.

An example of an implant with multiple axes of rotation is that of a first carpometacarpal joint for separating a trapezium bone from a first metacarpal bone. In this case, a translational movement of a saddle-shaped surface of a proximal part of the implant on the trapezium and a three-dimensional rotational movement of the distal part occur due to an articulated coupling, such as a spherical joint. An example of such an implant is described in WO 2017/137607 A2, while each of FR 2931059 A1 and f R 2805152 A1 can be considered as defining the preamble of claim 1.

In such an implant, the point of motion may be at or between two points, simultaneously or independently. Depending on the biomechanics of the joints into which the implant is inserted, the primary force of motion may shift rapidly and abruptly between the two points. Figures 1(a) and (b) illustrate a dual-axis implant that provides two axes of rotation: Ab-Ad (Axis 1) at the base of the metacarpal and Ex-Fl (Axis 2) on the surface of the trapezium to recreate the native axes of rotation of the joint. In Figure 1(a), a radiolucent stem is used to demonstrate the location of the ball and socket in the metacarpal.

Impingement on an orthopaedic implant can occur any time there is a decrease in space between the two elements causing one element to impact on the other, for example, the head of a hinged hemiarthroplasty impacting on the stem.

Uncontrolled impingement is a cause of poor implant outcomes. It also refers to uniaxial implants such as prosthetic hip arthroplasty; it can lead to instability, accelerated wear, and unexplained pain. Impingement is influenced by prosthetic design, component position, biomechanical factors, and patient variables. Uncontrolled impingement is linked to dislocation, and accelerated wear is derived from implant retrieval studies. Operative principles that maximize an impingement-free range of motion include proper combined acetabular and femoral anteversion and an optimal head-neck relationship. Operative techniques to prevent impingement include cup medialization to prevent component impingement and restoration of hip offset and length to prevent bony impingement.

To illustrate these issues, Figure 1(c) is an image from Brown TD, Callaghan JJ. Impingement in Total Hip Replacement: Mechanisms and Consequences. Curr Orthop. 2008;22(6):376-391. These images show the finite element analysis of a constrained line THA, showing the stress contours at the instant of incipient dislocation (A, B). Figure 1(d), also from Brown TD, Callaghan JJ. Impingement in Total Hip Replacement: Mechanisms and Consequences. Curr Orthop. 2008;22(6):376-391, shows a 3D finite element model of total hip dislocation, illustrating the initial relative position of the implant components (left), the stress on the acetabular component bearing surface during stable articulation (center), and the corresponding stresses just prior to a subsequent dislocation event (right).

The invention is directed to providing an improved implant with controlled impingement, or at least with reduced effects if impingement occurs.

Summary of the invention

The invention provides an implant as set forth in claim 1 and the appended claims 2 to 16.

The present disclosure includes bone joint implants. For example, the present disclosure includes a bone joint implant for a mammalian first carpometacarpal joint comprising a metallic proximal platform configured for translational movement about the trapezoid bone; a distal stem configured for intramedullary engagement with one end of the first metacarpal bone; an articulating engagement between the proximal platform and the distal stem; and a non-metallic proximal wear surface and a non-metallic distal wear surface.

In some embodiments described herein, the proximal non-metallic wear surface may form a cushioning surface that prevents contact between the proximal platform and the stem during articulation; may include a concave curvature; and/or may form an annular surface. The proximal platform may include a distal end surface having a convex curvature. In at least one embodiment, the distal non-metallic wear surface may be spherical in shape.

In some examples, the implant may include a unitary non-metallic wear member, and the proximal non-metallic wear surface and the distal non-metallic wear surface may be formed on the unitary wear member. The unitary non-metallic wear member may be an insert received in a proximal end surface of the stem, and the insert may include a proximal portion extending proximally of the proximal end surface of the stem. In some examples, the proximal portion may be a flange of the insert and the flange may include the proximal non-metallic wear surface, and/or the articulating coupling may be a ball and socket coupling, and the insert may form the socket of the ball and socket coupling.

The present disclosure also includes a bone joint implant for a mammalian first carpometacarpal joint, comprising a proximal portion configured for translational movement about the trapezium bone, the proximal portion including a platform; a distal portion configured for intramedullary engagement with an end of the first metacarpal bone, the distal portion including a stem and a wear surface located proximal to the stem; and an articulating coupling between the proximal and distal portions, the wear surface further located to limit articulation and prohibit contact between the platform and the stem. In at least one example, the wear surface may be non-metallic and the platform may be metallic. The wear surface may include a concave curvature and/or may form an annular surface. The platform may include a distal end surface having a convex curvature.

In some examples, the implant may include an insert received in a surface of the proximal end of the stem, wherein the wear surface is formed on the insert. The insert may include a proximal flange, wherein the wear surface is formed on the flange. Furthermore, the articulated coupling may be a ball and socket coupling, and the ball may form a portion of the proximal portion, and the socket may be formed by the insert. In at least one example, the ball may extend distally of the flange.

The present disclosure also includes a bone joint implant for a mammalian first carpometacarpal joint, comprising a proximal portion configured for translational movement about the trapezium bone, the proximal portion including a platform; a distal portion configured for intramedullary engagement with an end of the first metacarpal bone, the distal portion including a stem and an insert extending toward a proximal end of the stem, the insert including a flange extending proximal to the proximal end of the stem; and an articulated coupling between the proximal and distal portions, and the flange including a proximal end surface that limits movement between the proximal portion and the distal portion. In at least one example, the insert may be non-metallic and the platform may be metallic. The proximal end surface of the flange may have a concave curvature and/or the platform may include a distal end surface having a convex curvature. In at least one example, the flange may be annular. Furthermore, the articulated coupling may be a ball and socket coupling, the proximal portion may include the ball and the insert may include the socket, and/or the ball may extend distally from the flange.

The present disclosure also includes a bone joint implant for a mammalian first carpometacarpal joint, comprising a proximal portion configured for translational movement about the trapezium bone, the proximal portion including a metal platform having a proximal end surface having a concave curvature, and a distal end surface having a convex curvature; a distal portion configured for intramedullary engagement with an end of the first metacarpal bone, the distal portion including a metal stem and a non-metal insert extending toward a proximal end of the stem, the insert including a flange extending proximal to the proximal end of the stem; and a ball and socket coupling between the proximal and distal portions, the proximal portion including the ball, and the insert including the socket, and the flange including a proximal end surface that limits movement between the proximal portion and the distal portion. According to some examples, the proximal end surface may include a concave surface and/or the proximal end surface may be annular.

We describe in another exemplary aspect a bone joint implant for a first mammalian carpometacarpal joint, comprising

a metallic proximal platform configured for translational movement on the trapezoid bone;

a distal stem configured for intramedullary engagement with one end of the first metacarpal bone;

an articulated coupling between the proximal platform and the distal stem; and

a proximal non-metallic wear surface and a distal non-metallic wear surface.

Preferably, the proximal non-metallic wear surface forms a cushioning surface that prevents contact between the proximal platform and the stem during articulation. Preferably, the proximal non-metallic wear surface includes a concave curvature. Preferably, the proximal platform includes a distal end surface having a convex curvature. Preferably, the proximal non-metallic wear surface forms an annular surface. Preferably, the distal non-metallic wear surface is spherical in shape.

Preferably, the implant further includes a unitary non-metallic wear member, and the proximal non-metallic wear surface and the distal non-metallic wear surface are formed on the unitary wear member. Preferably, the unitary non-metallic wear member is an insert received in a proximal end surface of the stem, and the insert includes a proximal portion extending proximally of the proximal end surface of the stem. Preferably, the proximal portion is a flange of the insert, and the flange includes the proximal non-metallic wear surface. Preferably, the hinged coupling is a ball and socket coupling, and the insert forms the socket of the ball and socket coupling.

In another aspect we describe a bone joint implant for a first mammalian carpometacarpal joint, comprising:

a proximal portion configured for translational movement about the trapezoid bone, the proximal portion including a platform;

a distal portion configured for intramedullary engagement with one end of the first metacarpal bone, the distal portion including a stem and a wear surface located proximal to the stem; and an articulated coupling between the proximal and distal portions,

The wear surface is also located to limit articulation and prohibit contact between the platform and the stem.

Preferably, the wear surface is non-metallic and the platform is metallic. Preferably, the wear surface includes a concave curvature. Preferably, the platform includes a distal end surface having a convex curvature. Preferably, the wear surface forms an annular surface. Preferably, the implant further includes an insert received in a proximal end surface of the stem, the wear surface being formed on the insert. Preferably, the insert includes a proximal flange and the wear surface being formed on the flange. Preferably, the articulating coupling is a ball and socket coupling, and the ball forms part of the proximal portion and the socket is formed by the insert. Preferably, the ball extends distally with respect to the flange. Preferably, the wear surface includes a concave curvature.

We also describe a bone joint implant for the first carpometacarpal joint of a mammal, comprising:

a proximal portion configured for translational movement about the trapezoid bone, the proximal portion including a platform;

a distal portion configured for intramedullary engagement with one end of the first metacarpal bone, the distal portion including a stem and an insert extending to a proximal end of the stem, the insert including a flange extending proximal to the proximal end of the stem; and

an articulated coupling between the proximal and distal parts, and

The flange includes a proximal end surface that limits movement between the proximal portion and the distal portion.

Preferably, the insert is non-metallic and the platform is metallic. Preferably, the proximal end surface of the flange has a concave curvature. Preferably, the platform includes a distal end surface having a convex curvature. Preferably, the flange is annular. Preferably, the articulated coupling is a ball and socket coupling, and the proximal portion includes the ball and the insert includes the socket. Preferably, the ball extends distally with respect to the flange.

In other examples we describe a bone joint implant for a first mammalian carpometacarpal joint, comprising:

a proximal portion configured for translational movement about the trapezoid bone, the proximal portion including a metal platform having a proximal end surface having a concave curvature and a distal end surface having a convex curvature;

a distal portion configured for intramedullary engagement with one end of the first metacarpal bone, the distal portion including a metal stem and a non-metal insert extending toward a proximal end of the stem, the insert including a flange extending proximal to the proximal end of the stem; and

a ball and socket coupling between the proximal and distal portions, the proximal portion including the ball and the insert including the socket, and

The flange includes a proximal end surface that limits movement between the proximal portion and the distal portion.

Preferably, the proximal end surface includes a concave surface. Preferably, the proximal end surface is annular.

We also describe various aspects of bone joint implants that include:

a proximal part,

a distal part,

an articulated coupling between the proximal and distal parts, and

a cushioning interface configured to limit relative rotational motion about the coupling and/or to provide resilience for contact between the proximal and distal portions.

Preferably, the flange is made of a material that is more resilient than the material it comes into contact with. Preferably, the contoured surface of the flange is annular. Preferably, the flange is included in the distal portion.

Preferably, the flange is included in an insert within the distal portion.

Preferably, the flange has a thickness in the range of 0.5 mm and 4.0 mm, and more preferably in the range of 1.0 mm and 3 mm.

Preferably, the damping interface is made of a polymeric material. Preferably, the damping interface is made of a material that is non-metallic and is different from the material of a contact surface.

Preferably, the interface is configured to provide a cone of motion in the range of 30° to 50° of the distal portion relative to the proximal portion. Preferably, the insert includes an articulated coupling component.

Preferably, the coupling is a ball and socket coupling and the insert includes the socket of the coupling. Preferably, the insert comprises a locking element for snap-fitting into another component of the distal portion. Preferably, the locking element is a distal annular edge of the insert.

The implant may be configured for multi-axial movement. Preferably, the implant is configured for translational movement on a bone in one part and rotational movement in the other part about the articulated coupling.

The implant may be for a first carpometacarpal joint of a mammal, and the first portion is configured for translational movement in the trapezium bone and the distal portion is configured for intramedullary engagement with one end of the first metacarpal bone.

The interface may include a distally facing feature on the proximal portion. The distally facing feature may comprise a coating on the proximal portion. The coating may have a thickness in the range of 0.5 mm to 3.0 mm, and preferably 1.0 mm to 2.0 mm, and is preferably of a polymeric material. Preferably, the flange is part of an insert engaged in the first proximal portion or in the distal portion.

We also describe a bone-joint implant, in which:

The flange is made of a resilient material,

The flange has an annular contoured surface which mates with a bearing surface of a part when articulating the parts in use in extreme positions, and

The flange is on the distal part.

We also describe an insert for a bone joint implant comprising a proximal portion, a distal portion, and an articulated coupling between the proximal and distal portions, wherein the insert is configured to engage one of the portions and comprises a flange configured to limit relative rotational motion about the coupling.

Preferably, the insert is configured for an implant for a first mammalian carpometacarpal joint, wherein the first portion is configured for translational movement about the trapezoid bone and the distal portion is configured for intramedullary engagement with one end of the first metacarpal bone, and wherein:

the flange is made of a resilient material, and/or

The flange has an annular contoured surface that mates with a bearing surface of a part when articulating the parts in use in extreme positions, and/or

The insert is configured to engage the distal portion.

In one aspect, the implant is configured for uniaxial rotation. For example, the implant may be for a hip joint, a shoulder joint, or an elbow joint.

The cushioning interface may comprise a lining of a cavity, and said lining provides an interface surface for contact with a component such as a neck of the coupling.

Detailed description of the invention

The invention will be better understood from the following description of some embodiments thereof, given only by way of example with reference to the accompanying drawings in which:

Figures 1(a) and 1(b) are diagrams showing in the prior art different axes of movement of an implant for a first carpometacarpal joint to space a trapezium bone from a first metacarpal bone, as discussed above in the Introduction;

Figure 1(c) is a finite element analysis (FEA) diagram showing the prior art pinch point in a hip joint, and Figure 1(d) is an FEA diagram also of a hip joint showing the prior art pinch point and exit sites, also as discussed above in the Introduction;

Figure 2 is an image showing in perspective an implant of the invention, both the proximal and distal parts;

Figure 3(a) is a cross-sectional view through the distal portion of the implant, and Figure 3(b) is a perspective view of the stem of the distal portion, Figure 3(c) is a perspective view of the entire distal portion, and Figure 3(d) is a perspective view of the proximal portion;

Figure 4 is a set of views showing a portion of the distal portion of the implant, including top plan, end, perspective and cross-sectional views;

Figure 5 is a set of three pairs of end and sectional views showing the implant in different relative positions between its proximal and distal parts;

Figure 6 is a diagram illustrating the cone of motion allowed between the proximal and distal portions;

Figures 7(a) and 7(b) illustrate cross-sectional views of an implant, showing areas of material stress;

Figures 8(a) and 8(b) are sectional views showing an implant with an interface coating on the proximal portion; and

Figure 9 is a cross-sectional view of an implant for a hip joint, with a flange to increase surface area and reduce contact stresses.

Terms

“Intramedullary engagement” means engagement within a formed or existing medullary cavity in the bone, where the cavity is generally, but not exclusively, formed along a longitudinal axis of the bone. In one embodiment, the intramedullary engagement device comprises an interference fit screw or pin or stem, although other intramedullary devices are known. Typically, the screw is externally threaded. Smith & Nephew, Zimmer, Synthes, and other suppliers sell intramedullary devices. The engagement anchors the implant to the bone. In one embodiment, the medullary cavity is formed in a position that is offset in a volar direction. The medullary cavity may be formed in a position offset relative to the anatomical and/or biomechanical axis of the bone.

“Non-engaging bearing” means that the proximal portion is not fixed to the first bone, but is configured to bear on the end of the bone in a manner that allows translational movement of the bone. How this is achieved depends on the joint being treated and the specific anatomy of the first bone. As an example, where the joint is a carpometacarpal joint in the thumb, the end of the trapezium bone has a twisted saddle shape (see Figure 2 of Turker et al, Indian J Plast Surg. 2011, 44(2): 308-316) and the platform is configured to rest on this saddle and allow translational movement of the platform across the saddle. Thus, in this embodiment, the saddle-shaped curved platform typically has a concave-convex shape, having a concave curvature along a longitudinal aspect and a convex curvature along a lateral aspect. The saddle-shaped curved platform may have concave and convex curvature in both longitudinal and lateral aspects, i.e., in both length and width directions (as shown in Figures, e.g., Figures 2 and 4). This shape has been shown to provide an engagement that closely mimics the physiological situation and allows for a natural flexion-extension joint. When curvature is discussed in this disclosure (e.g., concave or convex), the reference point is from outside the structure (implant) or component, not from within the structure or component.

By “translational movement of the second bone relative to the first bone” is meant a non-pivoting movement of the second bone relative to the first bone. This can also be described as a sliding movement. An example is the involuntary translational movement of the metacarpal relative to the trapezium at the carpometacarpal joint of the thumb, which contributes significantly to the extension-flexion joint of the thumb. The implant of the invention facilitates such translational movement by employing a proximal portion that is configured to bear without engagement on the first bone.

“Articulating coupling” means a coupling that allows articulation between the first and second parts of the implant. The specific type of coupling employed in the implant depends on the joint being treated with the implant and, in some cases, the indication or severity of the indication. For example, where the implant is for the treatment of an arthritic hinge joint, for example, an elbow joint, the implant will generally comprise a hinge joint coupling. Where the implant is for the treatment of a saddle joint, for example, a carpometacarpal joint, the implant will generally comprise a ball-and-socket joint or a universal joint. “Controlled joint” means that the articulation is limited to specific types of joint.

“Supporting platform” means a base that rests on the end of the first bone (e.g., the end of the trapezium) such that translational (i.e., sliding) motion of the platform relative to the end of the bone is permitted. The bone is not fixed to the platform. The platform may be configured to conform to a surface on the top of the bone. In one embodiment, the platform is shaped to mimic an end of the second bone such that it allows for the same range of motion as the natural healthy joint, including translational motion. In the case of the carpometacarpal joint, where the end of the first bone (trapezium) has a crooked saddle topography, the platform may be shaped to conform to the crooked saddle to allow for one or more or all of the following ranges of motion of the first metacarpal relative to the trapezium, flexion, extension, abduction, adduction, internal rotation, external rotation, opposition, circumduction, and translation.

Description of the achievements

Referring to Figures 2 to 7, an implant 1 has a distal portion with an insert 100 on a stem 110 and a proximal portion 120.

In this case, the implant 1 is for a mammalian first carpometacarpal joint, as shown in Figure 1(a), for spacing a trapezium bone of the joint from a first metacarpal bone of the joint, while allowing translational movement of the first metacarpal bone relative to the trapezium bone. The distal portion 110 is configured for intramedullary engagement with one end of the first metacarpal bone. The proximal portion 120 has a saddle-shaped curved platform 122 with a proximally facing surface 124 for sliding over or through the trapezium bone. An articulated coupling (e.g., ball and socket) comprises a neck 123 joining the saddle 122 to a ball 121, as is known. This allows for controlled articulation of the trapezium and the first metacarpal bones.

The insert 100 has a cushioning interface feature (i.e. cushioning surface), in this case a flange 105 with a proximally facing contoured surface 101, which may be annular as shown in Figure 5. The flange 105 extends proximally of the stem, its contoured surface 101 being proximal and spaced from the proximal end of the stem 111. This enables it to play an important role arising from contact with the proximal portion in use, for example as a cushion. Distally from this surface is a shoulder 102 which acts as a key to engage the insert 100 on the stem 111 (see Figure 5) and prevent rotation of the insert on the stem, and surrounds a cavity 103 with a rim 106 for receiving the hinged coupling ball 121. There is a snap-on engagement of the ball 121 (see especially Figure 3(d) and Figure 5) in the cavity 103, behind the cavity rim 106, to allow assembly of a hinged hemiarthroplasty intraoperatively, and may also prevent disassembly of the device in vivo. The cavity may be centered or offset in any direction or angle as required.

Furthermore, distally, the insert 100 comprises an annular locking edge 104 for snap-fitting into a corresponding slot 116 of the recess 115 of the stem 111 receiving the insert 100. The engagement of the insert 100 on the stem 111 is effective due to the resiliency of the insert material and the fact that there is integral surface-to-surface contact in a snap-fit manner between the edge 104 and its corresponding engagement surface within the stem 111. This snap-fitting engagement of the insert 100 and the stem 111 allows for assembly of an articulated hemiarthroplasty intraoperatively, and may also prevent disassembly of the device in vivo. The insert is keyed by the shoulder 102 to prevent rotation and possible subsequent wear of the backing.

The flange 105 (and in this case the entire insert 100) is of a resilient polymeric material which is preferably a polymer, such as UHMWPE (in any form, possibly including vitamin E) or PEEK, in any form. In such case, the insert 100 may be referred to as a unitary non-metallic wear member.

Alternatively, it may be of other materials commonly used in orthopaedics, such as pyrocarbon (PyC) or ceramic, depending on the expected wear patterns of the construct. The insert 100 is of a material that is different from the metallic material of the unitary proximal portion 120 (saddle 122, neck 123 and articulating coupling ball 121), thus avoiding any galvanic type interactions that may cause excessive wear and/or chemical reactions leading to contaminants. Also, the (polymeric) material of the insert is different from the metallic material of the stem 111 for the same reasons. In general, metal to metal contact interfaces are avoided in the implant. While a polymeric material is good for wear, the biomechanical advantages of the flange, i.e. breaking the two axes of rotation, may be more important and as such the flange could be made of any suitable material. An example would be where the insert (or "liner") is made of a ceramic material, but the head is made of PEEK, which would still allow for a press-fit engagement for the articulating coupling. It is generally preferred that the flange and cavity not be of a relatively hard material, as that might not allow for a press-fit for anything other than a low modulus/high resilience material. This can be the other way around, for example if the head is a polymer and the liner is ceramic, the soft polymeric material can still press-fit into the hard ceramic cavity.

Thus, as discussed above, the implant 1 may include at least one non-metallic wear surface. The non-metallic wear surface may be present at any portion of the implant where a stem surface 110 and a platform surface 122 may engage, as shown in FIG. 5. In the case where the stem 110 includes an insert 100, the insert 100 may include at least one non-metallic wear surface. The at least one non-metallic wear surface may include a molded surface, for example, a surface with a convex curvature, and/or may form an annular surface. The platform may include a distal end surface having a corresponding shape, for example, concave. Alternatively, if the at least one non-metallic wear surface has a concave curvature, the platform may include a distal end surface having a convex curvature.

The resilience of the flange material is preferably sufficient to allow compression during use to the extent desired to achieve gradual conversion of motion between the axes. For this thumb implant, the thickness of the flange 105 is preferably in the range of 0.5 mm to 4.0 mm, and preferably 1.0 mm to 3.0 mm. The implant may be provided as a kit in which there is the proximal portion 122, the stem 111 of the distal portion 110, and a series of two or more inserts each of which fits onto the stem 111 but has a different flange thickness. The flange thickness sets the range of relative motion allowed, and in the example illustrated in Figure 6 is 40°. In general, the flange is preferably configured to provide a cone of motion in the range of 30° and 60° of the distal portion around the proximal portion. This allows the surgeon to choose the desired cone of motion. The implant thus achieves a predictable wear pattern. In addition, by reducing the cone of motion, the chances of dislocation are reduced. It should be noted that for this type of multiaxial joint, the full range of motion is actually about 80° when the sliding motion of the proximal part on the trapezium bone is taken into account. The illustration in Figure 6 is based on the fact that the proximal part is static, for illustrative purposes.

Furthermore, the contoured proximally oriented surface 101 of the flange 105 is configured to mate with a corresponding distal mating surface 125 of the saddle 122, to cause the movement of forces between the two axes of motion to be limited in a gradual manner, i.e., limiting movement between the portions 110 and 120. Thus, there is no abrupt change in force, or "change of direction" between the two axes. The mating surfaces 101 and 125 provide a large surface area for contact between the portions 110 and 120 as illustrated in Figures 5 and 7.

By having a load-bearing surface 101 interposed between the axes, forces are distributed in a more controlled, natural and physiological manner. Relative motion around the articulating coupling is limited in one example to approximately 40°, as illustrated in Figure 6. This range of motion is sufficient for use of the implant after deployment, but also helps to ensure that there are no excessive impact forces between the surfaces and that there is a smooth transition between the axes shown in Figures 1(a) and 1(b).

The snap-fit element 104 of the liner 100 allows for easy and efficient assembly onto the stem 111. In addition, the snap-fit cavity 103 of the liner facilitates the capture of a mating ball 121 to form the ball-and-socket joint in a manner that is advantageous due to the resilience of the material of the insert 100. As shown in the figures, the cavity 103 may be spherical in shape to receive the ball of the ball-and-socket joint.

The surface 101 of the flange 105 is contoured to match the geometry of the head component 120 to maximize surface contact and therefore minimize liner wear.

The insert 100 is replaceable from within the stem, i.e. it can be removed and another inserted in its place in the event of excessive wear. The insert 100 can be installed and/or removed with a suitable tool or tool set.

The insert 100 advantageously limits the extent of relative rotation in the abduction-adduction and flexion-extension planes. As shown in Figures 5 and 6, the saddle 122 has less freedom to rotate upward in this view and when contact is made with the surface insert 100, there is full surface contact between the saddle 122 and the contoured surface 101. Preferably, the contoured surface of the flange is tapered radially and distally and the corresponding mating surface of the saddle is tapered radially and proximally.

On the underside, as seen in Figure 5, there is a smaller meeting surface area, but the same effects and advantages apply. It will be appreciated that the insert 100 causes the pinching problem to be ameliorated. Of course, Figure 5 simply illustrates the coupling in a single plane, the plane of the page. As shown in Figures 3 and 4, the engaging surfaces 125 and 101 extend radially around the coupling (123, 121, 103) in an annular manner for support around 360°. The flange surface 101 has a mainly concave shape, albeit with a large radius; and the distal surface 125 of the saddle-shaped platform 122 has a mainly convex shape again with a large radius.

Referring to Figures 7(a) and 7(b), the shaded areas receive the maximum material stress between the sphere and cavity interface. In Figure 7(b), the saddle 122 of the proximal portion 120 is not in contact with the flange 105 of the insert 100. As a result, all of the material stresses are concentrated at the sphere and cavity interface (shown in Figure 7(b) as the stress region at the sphere 121). Figure 7(a) illustrates a portion of the proximal portion 120, e.g., the distally facing side of the saddle 125, in contact with the flange 105 of the insert 100 and the proximally facing surface 101. This increased contact area, shown as an additional stress region in Figure 7(a), allows for a broader distribution of material stresses. The insert 100 may be thicker at the portion with such increased contact area. This broader and more uniform distribution of the stress load on the implant 1 reduces the stress concentration at the interface of the sphere and the cavity, shown in sphere 121, and may extend the life of the implant 1.

Alternative examples

It is also envisioned that the implant may have a cushioning interface that provides a cushioning surface that includes a feature in addition to or instead of a flange, and/or that is not necessarily on an insert in the distal portion. For example, the proximal portion may have a cushioning interface on the surface facing the distal portion, which interface engages the distal portion with a large surface area. Such an interface may be a coating of a thickness in the range of 0.5 mm to 3.0 mm, and preferably 1.0 mm to 2.0 mm, for example. The interface is preferably of a resilient material, such as any of the polymers mentioned in the description above. In this case, it is envisioned that the distal portion may not have a flange in some examples, in which case the interface feature of the proximal portion engages directly to the stem of the distal portion.

Referring to Figures 8(a) and 8(b), an implant 150 is also for a thumb and comprises a distal portion with a stem 151 and an insert 152 for receiving a ball 153 of a proximal portion 154. The side facing the proximal portion 154 has a damping interface, i.e. a coating 157. This is provided to achieve at least some of the benefits of the flange of the previous embodiments. The coating 157 provides a damping effect which reduces the cone of motion and provides an increased surface area for distribution of forces along the construct.

The example of Figures 8(a) and (b) does not have a flange on the distal portion, but only an insert 152 for anchoring the articulated coupling on the stem 151, and therefore does not form part of the invention. However, it is preferred that the distal portion has a flange with a proximally facing, preferably contoured, surface spaced proximally from the stem for engagement with the proximal portion 154.

Alternative configurations to the examples in Figures 2 to 7

It is envisioned that the distal portion of the implant may include the physical features of the insert in an integral manner. Alternatively, the flange 105 may be provided as a discrete element. In addition, an insert could alternatively be threaded to engage the stem rather than be press-fitted.

A stem with an integrated flange may be made of a hard material and a coupling ball may be made of a softer material. The flange is located in relation to the base of the stem and the metacarpal bone.

The flange may be an integral part of the stem. Preferably, it would have the advantageous feature of having a contoured surface to provide a large surface area for contact with the mating part.

It is envisaged that, alternatively, there may be a resilient sphere and a high modulus cavity.

In the above examples, the contoured surface 101 of the flange mates with the distally facing surface 125 of the saddle 122, however, the surfaces may be configured differently. For example, the distally facing surface 125 of the saddle 122 may not have a convex curvature as shown in the figures.

The distraction distance, i.e. the distance between two bones after implantation of a device can be altered by increasing the height of the saddle head, as shown in Figures 5 and 6 for example. The cone of motion will not be affected, as the flange will have the same geometry. Alternatively, the flange can be thicker or thinner, which will affect the cone of motion. In some clinical uses, for example a patient who frequently dislocates an implant, a surgeon may choose during revision surgery to use a flanged insert with a very thick flange, to decrease the range of motion, potentially decreasing the likelihood of dislocation by increasing the jump distance (the distance a sphere must move out of a socket to dislocate).

It is envisioned that the insert can be attached to the stem without a mechanical/physical engagement feature and only have an adhesive bond.

Examples of uniaxial implants

As noted in the Introduction with reference to Figures 1(c) and (d), hip implants can have problems with liner impingement around the ball. We also describe an implant with a flange to improve hip implant outcomes.

Not within the scope of the invention, Figure 9 illustrates an implant having a neck 201 (only a portion of which is shown) with a sphere and a cavity 202 having a spherical internal cavity surface and having a flange 203 extending circumferentially around the cavity entrance protruding from the cavity. The material of the flange 203 is a resilient material such as UHMWPE, PEEK, ceramic or other material commonly used in orthopedic implants.

Flange 203 forms part of a liner for cavity 202, and the liner is attached to the remainder of the cavity portion (distal) by a press fit, cone, or other suitable locking mechanism. Flange liner 203 has a geometry with an interface surface 204 that matches that of the impinging component, in this case the neck 201 beneath the sphere. Flange 203 extends distally from cavity 202 to terminate at each end in an impact surface 204, for impact with neck 201.

As noted above, the insert is attached to the rest of the cavity portion by press fit, threads, or snap fit.

Figure 9 shows two positions for the neck 201, showing that there is an angular freedom of movement of approximately 110°. This arrangement improves the pinching forces on the cavity 202, dispersing the tension forces across the interface surface 204 and helping to prevent dislocation. Therefore, the flange 203 not only provides a much larger interface/contact surface 204, but is also of a more resilient material so that contact forces are absorbed.

As noted above, while a polymer liner and metal sphere is a preferred arrangement, there may alternatively be a metal liner and polyethylene sphere, a ceramic liner and polyethylene sphere, a polyethylene liner and ceramic sphere in any suitable combination depending on whether wear pattern or biomechanical axis management is more important.

The flange may be contoured to match the geometry of any part of a mating component. For example, in shoulder implants, the flange may be concave to optimally mate with the relative geometry of an implant neck. Similarly, in a hip implant, the flange may be convex to match the geometry of a neck component.

The distal part and proximal parts in total joint implants can be reversed depending on the joint and the implant.

The invention is not limited to the embodiments described, but may be varied in construction and detail within the scope of the claims.

Claims (16)

1. Bone joint implant (1) comprising: a proximal part (120), a distal portion (110) for intramedullary engagement with a bone, a coupling (103, 121, 123) articulated between the proximal and distal parts, in which, The proximal portion (120) is configured for translational movement over a bone, The implant is configured for multi-axial movement with translational movement on a bone by the proximal part (120) and rotation in the distal part (110) about the articulated coupling (121, 103), and The implant comprises a flange (105) extending radially and around at least a portion of the coupling and being configured (101) to limit relative rotational movement of the proximal and distal portions around the coupling, characterized in that The flange has a contoured surface (101) which mates with a bearing surface (125) of the proximal portion (122) when the parts are articulated in use in extreme positions. 2. The bone joint implant of claim 1, wherein the flange (105) is made of a material that is more resilient than the material of the proximal portion (120, 125) with which it comes into contact. 3. Bone joint implant according to claim 1 or 2, wherein the contoured surface (101) of the flange is annular. 4. A bone joint implant according to any one of claims 1 to 3, wherein the contoured surface (101) of the flange (105) is radially and distally tapered and the engaging and supporting surface (125) of the proximal portion is radially and proximally tapered. 5. A bone joint implant according to any one of claims 1 to 4, wherein the flange (105) is included in an insert (100) in a stem (111) of the distal portion (110), the flange extending proximally to the stem (111) and prohibiting contact between the proximal portion (120) and the stem (111) during articulation. 6. Bone joint implant according to any one of claims 1 to 5, wherein the flange has a thickness in the range of 0.5 mm and 4.0 mm, and optionally the thickness is in the range of 1.0 mm and 3.0 mm. 7. Bone joint implant according to any of the preceding claims, wherein the flange is made of a non-metallic material and is different from the material of a contact surface, and optionally the flange is made of a polymeric material. 8. A bone joint implant according to any of the preceding claims, wherein the flange is configured to provide a cone of motion in the range of 30° and 50° of the distal portion about the proximal portion. 9. The bone joint implant of any one of claims 5 to 7, wherein the insert includes a component (103, 106) of the articulating coupling, and wherein the coupling is a ball and socket coupling (121, 103, 106) and the insert (100) includes the socket (103, 106) of the coupling. 10. A bone joint implant according to any one of claims 5 to 9, wherein the insert comprises a locking feature (104) for snap-fitting onto the stem (111, 115, 116) and, optionally, the locking feature is a distal annular edge (104) of the insert (100). 11. A bone joint implant according to any of the preceding claims, wherein the implant is for a first carpometacarpal joint of a mammal, and the proximal portion is configured for translational movement on the trapezium bone and the distal portion is configured for intramedullary engagement with one end of the first metacarpal bone. 12. A bone articulation implant according to any one of claims 1 to 11, wherein the contoured flange surface (101) is a non-metallic annular wear surface that prohibits contact between a platform (122) of the proximal portion (120) and a stem (111) of the distal portion (110) during articulation. 13. The bone articulation implant of claim 12, wherein the proximal non-metallic wear surface (101) includes a concave curvature, and wherein the proximal portion platform (122) includes a distal end surface (125) having a convex curvature. 14. A bone joint implant according to any of the preceding claims, wherein the implant comprises a non-metallic distal wear surface (103) having a spherical shape. 15. A bone articulation implant according to any one of the preceding claims, wherein the flange (105) is an integral part of a unitary non-metallic wear member insert (100) configured for insertion into a stem (111) of the distal portion (110), said insert having a proximal non-metallic wear surface (101) for abutment with the proximal portion (120) in extreme articulation positions, and a distal non-metallic wear surface (103) for engagement with a surface of an articulation coupling component (121); and wherein the unitary non-metallic wear member is an insert (100) received in a proximal end surface of the stem (100), and the insert includes a proximal portion (105) extending proximally with respect to the proximal end surface of the stem, wherein said proximal portion is the flange (105) of the insert, and the flange includes the proximal non-metallic wear surface (101). 16. The bone joint implant of claim 15, wherein the articulating coupling is a ball and socket coupling, and the insert (100) forms the socket (103, 106) of the ball and socket coupling (121).